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Glucose in Serum (Fasting)

Published: August 9, 2026Updated: August 16, 2026

This test measures your blood sugar level after you haven’t eaten for at least 8 hours. It helps check for diabetes or other conditions affecting blood sugar.

Quick summary

["A fasting blood sugar test helps assess your risk for diabetes or monitor existing blood sugar control."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
33098-5
Short code
GA from FL.Chitty 1997
Synonyms
GA from FL.Chitty 1997
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
us-estimated-from-fl-chitty
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms like excessive thirst, frequent urination, unexplained weight changes, or fatigue. It’s also used during pregnancy, before surgeries, or to diagnose conditions like diabetes or hypoglycemia.

How the Test Works

A blood sample is taken from a vein, usually in your arm. The sample is sent to a lab where glucose levels are measured using an enzymatic method.

What to Expect Before the Test

Do not eat or drink anything except water for 8 hours before the test. Wear comfortable clothing and bring any medications you’re currently taking.

What to Expect During the Test

You’ll sit comfortably while a healthcare provider inserts a small needle into your arm to draw blood. The process usually takes a few minutes, and you may feel a slight pinch or sting.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Fasting Serum Glucose

Frequently asked questions

What does a normal fasting glucose level mean?
A normal fasting glucose level is generally considered below a specific threshold set by your healthcare provider, but this can vary. Your results will be interpreted in the context of your overall health.
How often should I get this test?
Your healthcare provider will determine how often you need this test based on your medical history, symptoms, and risk factors. Follow their recommendations closely.
Can I eat or drink anything before the test?
No, you must fast for 8 hours before the test. Only water is allowed during this period.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy